Quiet multivane multirow impeller for centrifugal pumps



Nov. 18, 1969 J, w. HENRY'IV QUIET MULTIVANE MULTIROW IMPELLER FOR CENTRIFUGAL PUMPS Filed Dec. 27, 1967 2 Sheets-Sheet 1 INVENTOR J0 N W. HENRYZF A GEN r I r I ATTORNEY Nov. 18, 1969 J. w. HENRY IV 3,

QUIET MULTIVANE MULTIRQW IMPELLER FOR CENTRIFUGAL PUMPS Filed Dec. 27, L967 2 Sheets-Sheet [EA- I L I I I/ v38 I fi I I I I 'I I I I I I I H I I I I\ I 128 24I l2 F/G. 2b.

F/G. 2c.

PULSATION (Pe)1 L TUDE I" 48 PUMP DEVELOPED HEAD PERIOD OF ONE REVILUTION INVENTOR JOHN W. HENRYIZ' AGENT BY p I7 ATTORNEY 3,478,691 QUIET MULTIVANE MULTIROW IMPELLER FOR CENTRIFUGAL PUMPS John W. Henry IV, Annapolis, Md., assignor to the United States of America as represented by the Secretary of the Navy Filed Dec. 27, 1967, Ser. No. 693,805 Int. Cl. F04d 29/22; F04b 21/00 US. Cl. 103115 4 Claims ABSTRACT OF THE DISCLOSURE The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to centrifugal impellers for centrifugal pumps and more particularly to multivane impellers having a plurality of axially spaced rows of output ports defined by equi-angularly spaced vanes extending from the input near the axis of the impeller to output at the peripheral edge of the impeller.

Conventional centrifugal pump impellers of the prior art generally have a small number of vanes defining ports or fluid passages in the impeller extending from near the axis of rotation to the peripheral edge and arranged equiangularly about the axis in a single row. In all centrifugal pumps, as each vane of the rotating impeller passes the discharge port of the pump casing, a pressure pulsation is produced and superimposed on the pumpdeveloped pressure head. This pulsation generates high level fluid-borne and structure-borne noise at a frequency corresponding to the period at which the vanes pass the discharge of the pump casing. The vane noise frequency may be computed by multiplying the number of vanes on the impeller by the rotational speed.

Vane frequency noise amplitude is a function of pump and impeller design parameters, including the number of vanes on the impeller. Noise amplitude may be decreased by increasing the number of vanes on the impeller since vane loading and hence the magnitude of the pressure pulsations that occur as the vanes pass the discharge port of the pump casing is reduced. In practice, however, a very large number of vanes is required to significantly reduce vane noise output, and a practical limit of the number of vanes is reached before obtaining any significant noise reduction. The ratio of flow restricting wetted surface area to a cross-sectional flow area increases rapidly with addition of vanes.

In commercial applications of centrifugal impeller pumps, vane frequency noise is generally not objectionable. However, vane frequency noise in centrifugal pumps aboard naval ships and submarines contribute substantially to the noise signatures emitted by these vessels and therefore reduction of noise from rotating machinery aboard these vessels is essential.

Prior art multivane impellers have been concerned with straightening the flow through the impeller and increasing efliciency but not with reduction of vane frequency noise.

United States Patent For example, multivane impellers with axially spaced rows of ports exist in the prior art, but the peripheral exit ports generally are not arranged to reduce pressure pulsations in the pressure head output,

SUMMARY The present invention provides a multivane impeller which substantially eliminates the fluid-borne and structure-borne vane frequency noise that is produced by most commercially available centrifugal impeller pumps. This reduction in noise is accomplished by providing a multi vane impeller with axially spaced and separated fluid passages in which the peripheral exit ports are angularly staggered from row to row according to the number of axially spaced rows. For example, the peripheral output ports of two axially spaced rows would overlap by onehalf the angular length of each port. In an impeller with three axially spaced rows, the angularly spaced output ports overlap by one-third the peripheral angular length. And in the case of four axially spaced rows the peripheral output ports overlap one-quarter of the peripheral length of the output port of each successive row. The output pressure is thereby smooth; that is, pressure pulsations are substantially eliminated in the toroidal chamber of the pump casing.

Accordingly, it is the principal object of this invention to provide an improved impeller for centrifugal pumps which substantially eliminates fluid-borne and structure-borne vane frequency noise.

Another object of this invention is to provide a multivane impeller for centrifugal pumps having a plurality of axially spaced rows of fluid paths.

Still another object of this invention is to provide a multivane impeller for a centrifugal pump which has equal or better efliciency than single row multivane centrifugal pump impellers.

Other objects and features of the invention will become apparent to those skilled in the art upon reference to the accompanying specification, claims and drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a section view of the impeller in line with the axis;

FIGS. 2a, 2b and 2c are diagrammatic and schematic edge views of the periphery of an impeller showing the staggering of vanes in relation to the axially spaced rows showing the overap of the peripheral output ports;

FIG. 3 is a plan view of the impeller along the section line 33 of FIG. 1 according to one of the embodiments of the invention;

FIG. 4 is 'a diagrammatic view and a graph showing the variation of pressure pulsations impressed upon the output pressure head of a centrifugal pump.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1, 2 and 3 there is shown a centrifugal pump impeller 10 according to this invention having fluid passages 12 defined by curved vanes 14. These curved vanes 14 extend from the radial input port 16, shown as smooth rounded edges at 18, to reduce turbulent flow. Curved vanes 14 curved outwardly to the periphery 20 in a backward direction in relation to the direction of rotation of the impeller as shown by arrow 22. The vanes 14 terminate at the periphery of the empeller at points 24 at an acute angle and are therefore sharply tapered to provide an uninterrupted peripheral surface 20.

As more clearly shown in FIG. 2a and FIG. 1, the multivane impeller, according to this invention, is provided with a plurality of axially spaced rows of fluid pas sages 12 defined by the impellers side plates 26 and 28 which are formed as an integral part of the body 30 of the impeller in the case of an impeller made by casting techniques. FIGS. 2b and 2c are schematic representations of three and four row impellers but are marked with like reference numerals.

The fluid passages 12 are separated by one or more disc-shaped separating members 38 extending from the intake port 16 to the periphery 20 which preclude communication between the fluid passages 12 of the axially spaced rows. These members are provided with a smooth leading edge 40 at the input to reduce turbulence.

The end plates 26 and 28 extend from the periphery 20 down to and smoothly join the cylindrical sealing surfaces 32 and 34 respectively. The cylindrical sealing surfaces 32 and 34 rotate within the serrated bores of the pump casing (not shown) so as to form labyrinth seals which are well known in the art. The axial bore 36 of the impeller is affixed to a pump shaft (not shown) which may be journaled in a pump casing (not shown) in any conventional manner.

DESCRIPTION OF THE OPERATION The multivane impeller according to this invention operates in the same conventional manner as prior art impellers having a single row of equi-angularly spaced fluid paths, however, the vane frequency noise output is considerably reduced. FIG, 4 shows in diagram and graph form the in situ condition which exist in commercially available centrifugal pumps using single row multivane impellers and existing to a considerably less degree in a pump casing using the present invention of an impeller having a plurality of rows. The empeller inducts fluid axially into its center port 16 where it is distributed by centrifugal force into and through the plurality of fluid passages 12 and exits into the toroidal chamber Where it will subsequently exit the pump casing at the discharge port 44. The pump by virtue of centrifugal force produces an average pressure head in the toroidal chamber 42 as shown by the dashed line 46 in both the diagram and the graph of FIG. 4. This pump-developed average pressure head is not actually of such a smooth and even pressure as indicated by the dashed line 46 but rather is actually produced by a varying pressure shown by dot-dash line 48 above and below the average pressure head having a period equal to the number of blades for each revolution of the pump impeller. Obviously, the frequency will rise as rotational speed is increased. The amplitude of the pulsation curve 48, shown as a dot-dash line in both the diagram and the graph, is a function of various design features such as the number of blades and the speed of rotation. The impeller, according to this invention, which has a plurality of rows of fluid passages, exhibits this same pulsation tendency but at greatly reduced amplitude and at a much higher frequency.

The amplitude of pulsations, and therefore the amount of fluid-borne and structure-borne vane frequency noise, is substantially eliminated in this invention by not only providing a plurality of axially spaced rows but by properly staggering the peripheral output ports of the fluid passages 12 as shown schematically in FIGS. 2a, 2b and 20. In the case of two axially spaced rows, proper staggering means that the tips 24 of the vane 14 in one row are centered on the length of peripheral ports measured between the vanes in the adjacent row; for three rows, the staggering of the tip 24 in the second row is positioned one-third the distance between the tips of the vanes in the first row and the tip of the third row is spaced twothirds the distance between the leading tip of the first row and the trailing tip. In the case of four axially spaced rows the tips of each successively adjacent row will be spaced in fourths along the length of the peripheral port in the first row. The aforementioned configuration can be readily understood by reference to FIGS. 2a, 2b and 2c which show an edge view of a two-row impeller and schematic view of threeand four-row impellers.

The fluid-borne and structure-borne noise reducing feature of the invention is obtained by the fact that the pressure pulses from adjacent rows of exit ports in the impeller add or cancel in such a manner as to give a smoother output in the toroidal chamber 42 thereby producing more pulses at less amplitude. While reduction of vane frequency noise is the primary object of this invention, other advantages obtain in using multivane impellers having a plurality of axially spaced rows. For example, there is little or no loss in efficiency when an impeller, according to this invention, is substituted in a pump casing for a conventional single row impeller. Also this impeller, employing a greater number of vanes as well as staggering, develops more pressure head than a conventional impeller of the same diameter without staggering, making possible the design of smaller diameter pump casings for pumps producing the same output pressure.

It should be understood, of course, that the foregoing disclosure relates only to the preferred embodiment of the invention and that numerous modifications or alterations, such as casting the impeller in an integral piece or building up the assembly from separate pieces, including the vanes, disc-shaped separating member and hub, may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims:

What is claimed is:

1. A unitary formed centrifugal pump impeller having a central hub for mounting on a shaft comprising:

a pair of axially spaced disc-shaped side plates extending from said hub, one of said plates defining a central inlet for the impeller;

a disc-shaped separator plate between said axially spaced side plates and axially spaced therefrom and spaced about said central inlet, thereby forming two co-planar axial rows for the attachment of vanes;

a plurality of radial equi-angularly spaced spirally curved vanes which form radially extending closed fluid paths in each of said co-planar rows, the vanes in each row being integrally attached to said separator plate and its adjacent side plate and being spaced from the axis of rotation of the impeller and communicating with said central inlet and extending to the outer periphery of said plates;

the direction of curvature and length of each of the vanes being the same;

the fluid paths in one row overlapping the fluid paths in the next row by an amount equal to one-half of the circumferential distance between the vanes which form said fluid paths,

whereby said integral construction and said overlap between the fluid paths cause said impeller to operate in a substantially noise free manner.

2. The device of claim 1 wherein each row of vanes has at least seven vanes.

3. A unitary formed centrifugal pump impeller having a central hub for mounting on a shaft comprising:

a pair of axially spaced disc-shaped side plates extending from said hub, at least one of said plates defining a central inlet for the impeller;

at least two disc-shaped separator plates between said axially spaced side plates and axially spaced therefrom, thereby forming at least three co-planar axial rows for the attachment of vanes;

a plurality of radial spirally curved equi-angularly spaced vanes which form radially extending closed fluid paths in each of said co-planar rows, the vanes in each row being integrally attached to its adjacent plates, communicating with said central inlet and extending to the outer periphery of said plates;

the direction of curvature and length of each of the vanes being the same;

the fluid paths in each row overlapping the fluid paths in the next adjacent row by an amount equal to the circumferential distance between the vanes which 5 form said fluid paths times the reciprocal of the numhas at least seven vanes.

References Cited UNITED STATES PATENTS 272,595 2/1883 Smith 230134.48 387,178 7/1888 Murphy 230l34.48

6 Davidson 30134.48 Murphy 103-115 Naegele et a1. Upson 230-134.45 Srogi. Stethem 103-115 Weil.

HENRY F. RADUAZO, Primary Examiner U.S. Cl. X.R. 

